In U.S. Pat. Nos. 5,844,086 and 6,005,076 (“Murray II”), assigned to the assignee hereof and the disclosures of which are incorporated herein by reference, there is described a process for the isolation of protein isolates from oil seed meal having a significant fat content, including canola oil seed meal having such content. The steps involved in this process include solubilizing proteinaceous material from oil seed meal, which also solubilizes fat in the meal and removing fat from the resulting aqueous protein solution. The aqueous protein solution may be separated from the residual oil seed meal before or after the fat removal step. The defatted protein solution then is concentrated to increase the protein concentration while maintaining the ionic strength substantially constant, after which the concentrated protein solution may be subjected to a further fat removal step. The concentrated protein solution then is diluted to cause the formation of a cloud-like mass of highly aggregated protein molecules as discrete protein droplets in micellar form. The protein micelles are allowed to settle to form an aggregated, coalesced, dense, amorphous, sticky gluten-like protein isolate mass, termed “protein micellar mass” or PMM, which is separated from the residual aqueous phase and dried.
The protein isolate has a protein content (as determined by Kjeldahl or equivalent method N×6.25) of at least about 90 wt %, is substantially undenatured (as determined by differential scanning calorimetry) and has a low residual fat content. The term “protein content” as used herein refers to the quantity of protein in the protein isolate expressed on a dry weight basis. The yield of protein isolate obtained using this procedure, in terms of the proportion of protein extracted from the oil seed meal which is recovered as dried protein isolate was generally less than 40 wt %, typically around 20 wt %.
The procedure described in the aforementioned patents was developed as a modification to and improvement on the procedure for forming a protein isolate from a variety of protein source materials, including oil seeds, as described in U.S. Pat. No. 4,208,323 (Murray IB), the disclosure of which is incorporated herein by reference. The oil seed meals available in 1980, when U.S. Pat. No. 4,208,323 issued, did not have the fat contamination levels of canola oil seed meals at the time of Murray II patents, and, as a consequence, the procedure of U.S. Pat. No. 4,208,323 cannot produce from such oil seed meals processed according to the Murray II process, proteinaceous materials which have more than 90 wt % protein content. There is no description of any specific experiments in U.S. Pat. No. 4,208,323 carried out using rapeseed (canola) meal as the starting material.
U.S. Pat. No. 4,208,323 itself was designed to be an improvement on the process described in U.S. Pat. Nos. 4,169,090 and 4,285,862 (Murray Iowa), incorporated herein by reference, by the introduction of the concentration step prior to dilution to form the PMM. The latter step served to improve the yield of protein isolate from around 20% for the Murray IA process.
In copending U.S. patent application Ser. Nos. 10/137,391 filed May 3, 2002 (US Patent Application Publication No. 20030125526) and 10/476,230 filed Jun. 9, 2004 (US Patent Application Publication No. 20040254353) (WO 02/089597), assigned to the assignee hereof and the disclosures of which are incorporated herein by reference, there is described a process for producing a protein isolate of high purity, containing at least about 100 wt % protein (N×6.25). In the aforementioned US patent application, the protein isolate is made by a process in which oil seed meal is extracted with a food grade salt solution, the resulting protein solution, after an initial treatment with a colourant adsorbent, if desired, is concentrated to a protein content of at least about 200 g/L, and the concentrated protein solution is diluted in chilled water to form protein micelles, which are allowed to settle to form an aggregated, coalesced, dense amorphous, sticky gluten-like protein isolate mass, termed “protein micellar mass” or PMM, which is separated from residual aqueous phase and may be used as such or dried.
In one embodiment of the process described above and as specifically described in U.S. patent application Ser. Nos. 10/137,391 and 10/476,320, the supernatant from the PMM settling step is processed to recover a protein isolate comprising dried protein from wet PMM and supernatant. This procedure may be effected by initially concentrating the supernatant using ultrafiltration membranes, mixing the concentrated supernatant with the wet PMM and drying the mixture. The resulting canola protein isolate has a high purity of at least about 90 wt %, preferably at least about 100 wt %, protein (N×6.25).
In another embodiment of the process described above and as specifically described in U.S. patent application Ser. Nos. 10/137,391 and 10/476,230, the supernatant from the PMM settling step is processed to recover a protein from the supernatant. This procedure may be effected by initially concentrating the supernatant using ultrafiltration membranes and drying the concentrate. The resulting canola protein isolate has a high purity of at least about 90 wt %, preferably at least about 100 wt %, protein (N×6.25).
The procedures described in the aforementioned US patent applications are essentially batch procedures. In copending U.S. patent application Ser. No. 10/298,678 filed Nov. 19, 2002 (US Patent Application Publication No. 20040039174) (WO 03/043439), assigned to the assignee hereof and the disclosure of which is incorporated herein by reference, there is described a continuous process for making canola protein isolates. In accordance therewith, canola oil seed meal is continuously mixed with a salt solution, the mixture is conveyed through a pipe while extracting protein from the canola oil seed meal to form an aqueous protein solution, the aqueous protein solution is continuously separated from residual canola oil seed meal, the aqueous protein solution is continuously conveyed through a selective membrane operation to increase the protein content of the aqueous protein solution to at least about 200 g/L while maintaining the ionic strength substantially constant, the resulting concentrated protein solution is continuously mixed with chilled water to cause the formation of protein micelles, and the protein micelles are continuously permitted to settle while the supernatant is continuously overflowed until the desired amount of PMM has accumulated in the settling vessel. The PMM is removed from the settling vessel and may be dried. The PMM has a protein content of at least about 90 wt % (N×6.25), preferably at least about 100 wt %.
In such procedures, canola protein isolate is recovered by dilution with chilled water of a concentrated protein solution to precipitate PMM. In addition, further canola protein isolate may be recovered from the supernatant from the PMM precipitation step.
As described in copending U.S. patent application Ser. No. 11/038,086 (US Patent Application Publication No. 20050181112) (WO 2005/067729), assigned to the assignee hereof and the evidence of which is incorporated herein by reference, the supernatant from the PMM precipitation step may be heat-treated to cause precipitation of 7S and 12S proteins from the supernatant. The 2S protein subsequently recovered from the heat-treated supernatant, has a improved solubility in aqueous media at a variety of pH values and is able to provide improved clarity in solution with soft drinks, thereby providing clear protein fortified soft drinks.